[P-EM09] Dynamics of Magnetosphere and Ionosphere

[PEM09-03] Fast Magnetic-Field Annihilation in Electron-scale Current Sheet in Earth's Magnetotail

*Hiroshi Hasegawa¹, Richard E. Denton², Kevin J. Genestreti³, Takuma Nakamura⁴, Tai D. Phan⁵, Rumi Nakamura⁴, Kyoung-Joo Hwang⁶, Narges Ahmadi⁷, Quanqi Shi⁸, Michael Hesse⁹, James L. Burch⁶, James M. Webster⁶, Roy B. Torbert¹⁰, Barbara L. Giles¹¹, Dan J. Gershman¹¹, Christopher T. Russell¹², Robert J. Strangeway¹², Hanying Wei¹², Per-Arne Lindqvist¹³, Yuri V. Khotyaintsev¹⁴, Robert E. Ergun¹⁵, Yoshifumi Saito¹ (1.Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 2.Department of Physics and Astronomy, Dartmouth College, 3.Southwest Research Institute, Durham, 4.Space Research Institute, Austrian Academy of Sciences, 5.Space Sciences Laboratory, University of California, Berkeley, 6.Southwest Research Institute, San Antonio, 7.Laboratory for Atmospheric and Space Physics, University of Colorado, 8.Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, 9.Space Plasma Physics Group, University of Bergen, 10.Physics Department, University of New Hampshire, 11.NASA Goddard Space Flight Center, 12.Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, 13.Royal Institute of Technology, Stockholm, 14.Swedish Institute of Space Physics, 15.Department of Astrophysical and Planetary Sciences, University of Colorado)

Keywords:magnetic reconnection, magnetotail, magnetic field annihilation

Magnetic reconnection in current sheets is the key to fast release of magnetic energy in many space and astrophysical plasma systems, such as during magnetospheric substorms, but observations to understand exactly how magnetic-to-electron energy conversion occurs in electron-scale diffusion regions (EDRs), where magnetic topology changes, have been lacking. It is generally believed that EDR has an X-type magnetic-field geometry around which the energy of anti-parallel magnetic fields is mostly converted to the bulk-flow energy of electrons by magnetic tension of reconnected field-lines. We present state-of-the-art analysis of multi-spacecraft observations in Earth's magnetotail of an electron-scale current sheet, which demonstrates that contrary to the standard model of reconnection with an X-type EDR geometry, the fast energy conversion in the detected EDR was caused mostly by magnetic-field annihilation, rather than reconnection. The experimental discovery of the annihilation-dominated EDR reveals a new form of energy conversion in the reconnection process that can occur when the EDR has evolved from the X-type to planar geometry.